There has recently been proposed a magnetic refrigeration system as a substitute for a conventional gaseous refrigeration system using fluorocarbon gas as a cooling medium, which gas induces environmental problems including global warming.
The magnetic refrigeration system employs a magnetic refrigeration material as a refrigerant, and utilizes magnetic entropy change occurred when the magnetic order of the magnetic material is changed by magnetic field under isothermal conditions, and adiabatic temperature change occurred when the magnetic order of the magnetic material is changed by magnetic field under adiabatic conditions. Thus, freezing by the magnetic refrigeration system eliminates the use of fluorocarbon gas, and improves refrigeration efficiency compared to the conventional gaseous refrigeration system.
As a magnetic refrigeration material used in the magnetic refrigeration system, Gd (gadolinium)-containing materials are known, such as Gd and/or Gd compounds. The Gd-containing materials are known to have a wide operating temperature range, but exhibit a disadvantageously small magnetic entropy change (−ΔSM). Gd is a rare and valuable metal even among rare earth elements, and cannot be said to be an industrially practical material.
Then, NaZn13-type La(FeSi)13 compounds are proposed as having a larger magnetic entropy change (−ΔSM) than the Gd-containing materials. For further improvement in performance, for example, Non-patent Publication 1 discusses various substitution elements, including cobalt (Co) substitution, and Patent Publication 1 proposes partial substitution of La with Ce and hydrogen adsorption to give La1-zCez(FexSi1-x)13Hy and increase the Curie temperature. Patent Publication 2 proposes adjustment of a Co—Fe—Si ratio in La (Fe1-x-yCoySix)13 to expand the operating temperature range.
Further, as means for producing these materials, for example, Patent Publication 3 proposes solidification by rapid cooling on a roll, Patent Publication 4 proposes resistance-sintering under pressurizing, and Patent Publication 5 proposes reaction of Fe—Si alloy with La oxide.    Patent Publication 1: JP-2006-089839-A    Patent Publication 2: JP-2009-221494-A    Patent Publication 3: JP-2005-200749-A    Patent Publication 4: JP-2006-316324-A    Patent Publication 5: JP-2006-274345-A    Non-patent Publication 1: “Jiki Reito Gijutsu no Jo-on-iki heno Tenkai (Magnetic Refrigeration near Room Temperature)”, Magune, Vol. 1, No. 7 (2006)